. >> they're designed and used for short-haul uses of passengers so they may take off and land three five, seven, 10 times a day sometimes. so their landing gear are put under a lot more stress. >> reporter: today bombardier said it would support any investigation. dean reynolds, cbs news, chicago. >> couric: in health news, there's been a lot of debate about what causes attention deficit hyperactivity disorder, commonly called a.d.h.d. some say it has to do with diet. others suggest parenting may be to blame. but today, for the first time, researchers say they found a definitive link between a.d.h.d. and a genetic mutation. here's dr. jon lapook. >> thanks, mom. >> reporter: carol siege always suspected a.d.h.d. ran in her family. all four of her sons have been diagnosed. >> people going through the experience, it makes perfect sense to them. >> reporter: today's news confirming a genetic link comes as a relief to parents of kids with a.d.h.d. >> it's wonderful because it's been so obvious to us. and so it takes away that-- the blame and the shame that you feel as a parent. >> repor